Human neutrophils and monocytes are attracted to sites of inflammation and engulf invasive microorganisms or host cell debris. These phagocyte responses are mediated by surface receptors for a variety of substances released by infective agents or host cells, or derived from host plasma. The purpose of this project is to define the biochemical structure and transduction mechanisms of some of these surface receptors. More specifically, the present studies focus upon: (i) the receptor for bacterially derived formyl peptides, the formyl peptide chemotactic receptor (FPCR), (ii) pertussis toxin inhibitable GTP binding regulatory proteins (Gi) in myeloid cells required for FPCR and other receptor mediated cellular responses; (iii) the iC3b (CR3) receptor and other surface antigens on neutrophils. Using affinity labelling, we showed that FPCR contains both complex- and high mannose-type N-linked polysaccharides. We showed that FPCR appears at the late promyelocyte stage of myeloid differentiation accompanied by functional responses to formyl peptide. Using antibodies and oligonucleotide probes to detect protein and mRNA of different alpha subunits of GTP regulatory proteins, we showed that myeloid cells contain at least two subtypes of Gi and do not contain the Gi subtype most common in brain tissue. The presence of distinct subtypes of Gi may be important for neutrophil functions mediated by different receptors. With immunogold-electron microscopy we showed that the density of neutrophil surface CR3 doubles after stimulation with phorbol myristate acetate and that CR3 are clustered on the cell surface. This arrangement may be important for the neutrophil adherence mediated by this receptor.